OLEDs are useful in a variety of applications as discrete light-emitting devices, or as the active element of light-emitting arrays or displays, such as flat-panel displays in watches, telephones, laptop computers, pagers, cellular phones, calculators, and the like.
Conventional OLED display structures are built on glass substrates in a manner such that a two-dimensional OLED array for image manifestation is formed. Each OLED in the array generally includes overlying layers, starting with a light-transmissive first electrode formed on the substrate, an organic electroluminescent (EL) emission medium deposited over the first electrode, and a metallic electrode on top of the organic electroluminescent medium. When an electrical potential is placed across the electrodes, holes and electrons are injected into the organic zones from the anode and cathode, respectively. Light emission results from hole-electron recombination within the device.
Two primary technical challenges relating to OLED technology are materials and fabrication. Materials science, whether related to small molecules or polymers, holds the key to the industry's ability to improve lifetime and emission efficiency. Furthermore, given that the organic materials cannot come in contact with water or oxygen, fabrication is especially difficult. Well known shadow masked based vacuum deposition technology, using conventional vacuum chambers, is often used for manufacturing OLEDs. However, shadow mask based vacuum deposition technology is limited in the precision of the deposition geometry.
A laser thermal transfer (LTT) process is an example of an emerging technology for manufacturing OLEDs with potential advantages over conventional deposition processes. LTT is a process that uses heat to transfer an organic donor material (emitter material that is being transferred) onto a substrate. The donor material and substrate are held in a predetermined spatial relationship with respect to one another. The donor material includes a support layer, a thermal absorber layer and a layer of electroluminescent organic material. The LTT process includes using a laser beam that generates heat by impinging upon the absorber layer of the donor material, thereby creating heat, which vaporizes the organic material, which is subsequently deposited upon the target substrate in a predefined pattern. For example, U.S. Pat. No. 6,582,875 describes the process of using a multichannel laser print head, which transfers organic material to a patterned substrate. Several technical challenges exist for manufacturing OLEDs using the LTT process, such as implementing process monitoring and control techniques for ensuring a high-quality OLED structure. For example, visual artifacts can result if the print head is not properly aligned with the patterned substrate, or if the motion of the print head is not properly coordinated relative to the patterned substrate.
For example, U.S. Pat. No. 5,994,836 describes an organic light-emitting diode (OLED) array structure, and corresponding method of making the structure. Each OLED pixel includes a first electrode on a substrate, a second electrode on a substrate, and an organic emission layer disposed between the first and second electrodes so as to emit visible light when a suitable potential is applied thereto by the electrodes. In accordance with certain embodiments of this invention, a step covering or coverage layer is provided over step or edge areas of the first electrode in order to reduce the structure's susceptibility to breakdown at pixel edges, thereby improving yields. While U.S. Pat. No. 5,994,836 describes a suitable method of manufacturing an OLED structure, it provides no mention of process monitoring, in particular, process monitoring of an LTT process for manufacturing OLEDs.